although certainly more democrats are pro gay marriage than republicans, there are sizeable numbers of "religiously inclined" people in both parties who believe that gay marriage is a violation of scripture - whether that book is the bible, the talmud, or the quran. this isn't a question of where you are on the political continuum. examples abound of left wing governments which arrest, hang, and otherwise harass those perceived to be gay, let alone simply not endorsing gay marriage.
if your religion says gay marriage is an abomination, or interracial marriage, or interfaith marriage, then your rock of gibraltar is simply going to have to be that church, since in secular american society we don't impose such shibboleths, by acclaim or any other means.
i'm perfectly okay with anyone being gay - even toe tapping republicans in airport bathrooms - which is evidently some sort of taboo to those on the political left. hypocrisy abounds both in the toe tapper, and those who want to make an example of him